Introduce TabGroup sharing

This CL adds an item in TabGridDialog toolbar menu to expose tab group
sharing. The group is shared as plain text which is in the format of
a list of URLs of all tabs in the group.

Bug: 1017492
Change-Id: I65c89f56bbd4f6135501958e5a925c5bbc6c2ac0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900303
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734750}
11 files changed